🧱 libft — 42 Paris Project

Rebuilding the fundamental bricks of the C standard library and creating a personal reusable library for all future 42 projects.

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🎓 Context

This project is one of the very first steps of the 42 Paris curriculum.
Its goal is to reimplement essential C standard library functions (strlen, memcpy, strchr, etc.) as well as a few extra utilities, in order to build a personal base library: libft.

This library will be reused in all upcoming 42 projects (like ft_printf, minishell, push_swap, etc.) and serves as the foundation for all future C exercises.

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⚙️ Objective

• Recreate basic string, memory, and character manipulation functions.
• Implement additional utility functions (ft_split, ft_strjoin, ft_itoa, etc.).
• Add linked list management functions (ft_lst*) for the bonus part.
• Provide a reliable, optimized, and memory-leak-free static library.

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🗂️ Repository structure

libft/
├── Makefile                     # Compiles the lib, tests, and memcheck binaries
├── libft.h                      # Main header file
├── ft_*.c                       # All lib functions (mandatory + bonus)
├── subject/                     # Official 42 subject
│   └── 2022.libft.en.subject.pdf
└── tests/
    ├── mandatory_unit_tests/    # Criterion tests for mandatory functions
    ├── bonus_unit_tests/        # Criterion tests for bonus functions
    ├── mandatory_memcheck.c     # Main for memory leak tests (mandatory part)
    ├── bonus_memcheck.c         # Main for memory leak tests (bonus part)
    └── run_*                    # Generated executables (tests & memcheck)

The naming strictly follows 42 subject conventions:
ft_functionname.c for each function and libft.h as the main entry point.

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🧰 Available Make commands

Command	Description
make	Build libft.a (mandatory functions only).
make bonus	Add bonus objects (ft_lst*) to libft.a.
make test	Build & run Criterion tests (mandatory).
make test_bonus	Build & run Criterion tests (mandatory + bonus).
make leaks	Build a memcheck binary (mandatory) and run leaks (macOS) or valgrind (Linux).
make leaks_bonus	Same as above for the bonus part.
make clean	Remove only object files (.o).
make fclean	Remove all objects and binaries (libft.a, run_tests, run_memcheck).
make re	Clean everything and rebuild from scratch.
make help	Display available commands, OS detection, compiler flags, and Criterion libraries.

💡 make help also displays:

• The detected OS (macOS / Linux)
• The Criterion flags and linked libraries
• A summary of all useful targets

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🧪 Unit tests

All tests are written using the Criterion framework.
They check each function independently, including edge cases and segmentation faults.

Two test suites exist:

• mandatory_unit_tests/ → standard libc-like functions
• bonus_unit_tests/ → linked list (ft_lst*) functions

📦 Compilation

make test
# or
make test_bonus

🧹 Memory leak verification

make leaks
# or
make leaks_bonus

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🔧 Installing dependencies

🧪 Criterion

macOS (via Homebrew)

brew install criterion

Ubuntu / Debian

sudo apt update
sudo apt install libcriterion-dev

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🧠 Memory check tools

macOS

leaks is included with the Xcode Command Line Tools.

xcode-select --install

Ubuntu / Debian

sudo apt install valgrind

The Makefile automatically detects the correct tool using uname:

• macOS → uses leaks
• Linux → uses valgrind

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“Build your own standard library, and you’ll never fear undefined behavior again.” 🙃